Screw compressors used in water cooled chillers are of the oil flooded type. Oil provides a seal between adjacent trapped volumes during the compression process and an oil separator removes oil from the hot, compressed gas downstream of the compression process. At high speeds, the percentage of gas leakage between the rotor and housing and interlobes is small as compared to the inlet flow. This is partly due to the oil film formed between the rotor and housing. Additionally, to reduce drag loses, the amount of oil injected should be kept at a minimum. For screw compressors the loading or flow is directly proportional to speed. At low speeds the sealing at the tips and interlobes is poor which reduces the volumetric efficiency of the compressor.